Process for preparing hydroxy-substituted esters of phosphorodithioic acids



United States Patent 3,361,856 PROCESS FOR PREPARING HYDROXY-SUB-STHTUTED ESTERS 0F PHOSPHORODI- TliHOIC ACIDS William M. Le Suer,Cleveland, Ohio, assignor to The Lubrizol Corporation, Wicklitie, Ohio,a corporation of Ohio N0 Drawing. Filed Dec. 13, 1963, Ser. No. 330,2256 Claims. (Cl. 26t)978) This invention relates to the chemistry oforgano phosphorus compounds and more particularly, to the chemistry ofphosphorodithioic acids. Still more particularly it relates to a processwhereby these acids are converted to neutral hydroxy-substitutedtriesters of phosphorodithioic acids.

The development of petroleum lubricating oils has been toward the use ofmore etficient refining methods to reduce the sludging tendency of suchoils. These highly refined oils, however, have decreased resistance tooxidation and are more likely to form soluble acidic oxidation productswhich are corrosive, particularly under severe service conditions.Although generally superior to lightly refined oils they tend to form avarnish film on hot metal surfaces, such as the cylinder walls andpistons of an internal combustion engine, under very severe engineoperating conditions.

This invention is a process for making products which can be formulatedwith highly refined petroleum fractions to give improved motor oils andgear lubricants. In such formulation, the products of this process serveboth as corrosion inhibitors and also as extreme pressure agents. Forexample, the addition of a small proportion of the product of thisprocess to a refined lubricating oil greatly reduces the tendency ofsuch oil to corrode metal surfaces, especially those of copper-lead andsilver-lead bearings. In addition, gear lubricants which are subjectedto extreme pressure conditions are greatly improved by the addition ofthe products of this process so that they may better withstand theextreme pressures of the environments in which they are used.

In addition to the desirability of these products as corrosioninhibitors and as extreme pressure agents, they are particularly usefulin lubricating formulations because of their compatibility with otherknown lubricant additives.

Furthermore, these products are useful as ore floatation agents and asmetal finishing agents. They are also valuable as starting materials forthe preparation of still other effective lubricant additives.

It is a principal object of the invention to provide a novel process forthe preparation of certain lubricant additives and lubricant additiveintermediates.

It is also an object of the invention to provide a convenient processfor the preparation of neutral phosphorusand sulfur-containingcompositions.

These and other objects are accomplished by the process which comprisesreacting a salt of a phosph-orodithioic acid having the structuralformula (RO) PSSH NR' wherein R is a hydrocarbon radical and R isselected from the class consisting of hydrogen and hydrocarbon radicals,with at least about an equivalent amount of an organic compound selectedfrom the class consisting of epoxides and thioepoxides, in the presenceof an acidic compound, which is weaker in acidity than the dialkylphosphorodithioic acid which is used. The product of this reaction is ahydroxy-substituted triester of phosphorodithioic acid.

The hydrocarbon radicals of the above structure may be aliphatic oraromatic and are substantially hydrocarbon in character. Illustrativetypes of such radicals include alkyl, cycloalkyl, aryl, aralkyl,'alkaryl, alkenyl, cycloalkenyl, etc.

The phosphorodithioic acids from which the hydroxysubstituted triesterscan be derived are well known. They may be prepared by the reaction ofphosphorus pentasultitle with a hydroxy compound which corresponds tothe organic radical R. This reaction is illustrated by the action ofphosphorus pentasulfide on ethyl alcohol to produce0,0'-diethylphosphorodithioic acid. In similar fashion, aliphatichydroxy compounds such as propyl, butyl, isobutyl, amyl, hexyl,cyclohexyl, n-octyl, iso-octyl, lauryl, etc., alcohols or aromatichydroxy compounds such as phenol, alkylated phenols, naphthols,alkylated naphthols, and the like may be reacted with phosphoruspentasulfide to produce phosphorodithioic acids of utility as startingmaterials for the present invention.

The reaction of phosphorus pentasulfide with a mixture of alcohols orphenols (e.g., isobutanol and n-hexanol in 2:1 weight ratios) results inphosphorodithioic acids in which the two organic radicals are different.Such acids likewise are useful herein.

The substituted ammonias or amines useful for forming thephosphorodithioic acid salts of this invention may be aliphatic amines,aromatic amines, or cyclo-aliphatic amines. Amines having from 1 toabout 15 aliphatic carbon atoms are preferred. Methyl amine, ethylamine, n-propyl amine, isopropyl amine, n-butyl amine, isob-utyl amine,secondary butyl amine, tertiary butyl amine, n-arnyl amine, isoamylamine, n-heptyl amine, n-hexyl amine, octyl amine, nonyl amine, decylamine, hendecyl amine, dodecyl amine, tridecyl amine, tetra-decyl amine,pentadecyl 'amine, dimethyl amine, diethyl amine, di-npropyl amine,diisopropyl amine, dibutyl amine, diamyl amine, dihexyl amine, trimethylamine, triethyl amine, benzyl amine, pyridine, morpholine, ethylenediamine, piperazine, cyclopentyl amine, and diethylene triamine arespecific examples of useful amines.

When an ammonium phosphorodithioate is reacted with an epoxide in thepresence of a weaker acid, said weaker acid has the function ofcombining with the liberated ammonia. For this purpose, it must be oflower acidity than the phosphorodithioic acid in order not to displacethe phosphorodithioic acid from its ammonium salt before its reactionwith the epoxide. Suitable acids, therefore, are those which have a pKvalue greater than that of the phosphorodithioic acid which is about 1.Examples of such acids are: aliphatic carboxylic acids such as, formic,acetic, propionic, butyric, s-uccinic, malic, ascorbic, .gl-utaric,etc.; aromatic carboxylic acids such as benzoic, toluic, etc.; weakerinorganic acids such as sulfurous, boric, nitrous, carbonic, etc.; andacidic gases such as CO H 8, S0 etc.

The ammonium salt or substituted-ammonium salt of a phosphorodithioicacid may be prepared by adding an equivalent amount of ammonia or asubstituted ammonia to the acid, or a solution of the acid in an inertsolvent, to obtain the neutral salt, as illustrated by the followingequations:

Similarly, the ammonium salt or substituted ammonium salt of aphosphorodithioic acid may be prepared by the 3 reaction of the acidwith the ammonium salt of a weaker acid than the phosphorodithioic acid.This may be represented by the following equations:

(RO PSSH+NH OOC CH The reaction of a phosphorodithioic acid with ammoniais exothermic and may be carried out at tempera tures within the rangeof from about 35 C. to the decomposition temperature of the salt, orabout 200 C. It is the usual procedure to start passing ammonia into theacid at about 20 C.60 C. and to allow the temperature to rise to about90l00 C., keeping the tem perature of the reaction at about 100 C. bycontrolling the rate of ammonia addition and by external cooling ifnecessary.

The reaction of a phosphorodithioic acid with the ammonium salt of aweaker acid is also exothermic and may be carried out at temperatureswithin the range of from about C. to the decomposition temperature ofthe salt, or about 200 C. It is usually carried out by adding aconcentrated aqueous solution of the ammonium salt of the weaker acid tothe phosphorodithioic acid at 20 C. to about 40 C. and keeping thetemperature of the reaction below about 60 C. by controlling the rate ofaddition of ammonium salt and by external cooling if necessary.

Most of the ammonium and substituted ammonium phosphorodithioates arecrystalline salts at room temperature. This property affords thedistinct advantage of being able to purify the amine phosphorodithioatesby recrystallization from a suitable solvent before further reaction andthus obtaining very pure hydroxy-substituted triesters.

As stated previously, the weaker acid, which is present during thereaction of the ammonium phosphorodithioate with an epoxide, has thefunction of removing the byproduct ammonia as it is formed. Thus, inorder to combine with all of the ammonia formed, the amount of weakeracid to be used must be equivalent to the amount of ammonia in thephosphorodithioate salt. However, part or nearly all of the ammonia maybe removed from the epoxide-ammonium phosphorodithioate reaction bypassing an inert gas such as nitrogen through the reaction mixtureduring the epoxide addition. In such instances it is necessary to useonly a relatively small amount of the weaker acid near the end of thereaction to scavenge the remaining ammonia which, in many instances, isotherwise difiicult to remove.

A particularly advantageous embodiment of this invention is effected byreacting a dialkyl phosphorodithioic acid with an equivalent amount ofan ammonium salt of a weaker acid thus forming an ammoniumphosphorodithioate and the free weaker acid. An epoxide is thenintroduced into the mixture forming the hydroxy-substituted trister ofphosphorodithioic acid and regenerating the ammonium salt of the weakeracid which can then be separated and recycled for reaction with more ofthe phosphorodithioic acid.

The reaction of the ammonium and substituted ammonium phosphorodithioatesalts with an epoxide is somewith exothermic, especially in the presenceof a weaker acid. The temperature, however, is easily controlled by therate of addition of the epoxide. Although it is not necessary, it ispreferred to control the temperature of the reaction mixture so that itis reasonably constant throughout the course of the reaction. Thetemperature of the reaction may be as low as -60 C. or lower, and on theother hand, it may be as high as 200 C. or even higher. Generally, forreasons of economy, it is preferred to carry out the process at asufiiciently high temperature that the ammonium salt of thephosphorodithioic acid is a liquid 4- rather than to react the epoxidewith a solution of the ammonium salt at a lower temperature.

The organic epoxides and thioepoxides may be represented by thestructural formula wherein R" is a hydrocarbon radical or hydrogen, X issulfur or oxygen, and n is 1 or 0. Those epoxides and thioepoxides arepreferred in which one of the carbon atoms attached to oxygen or sulfuris also attached to two hydrogen atoms. In other words, the preferredepoxides and thioepoxides are terminal epoxides. These have been giventhe name terminal epoxides and thioepoxides because they may be thoughtof as being derived in most instances, from a vinyl compound which has aterminal olefinic double bond.

The term epoxide is used hereafter in a broad sense to denote theepoxides and the thioepoxides.

Specific examples of suitable epoxides include ethylene oxide, propyleneoxide, epichlorohydrin, l-butene oxide, butadiene monoxide, l-amyleneoxide, styrene oxide, ethylene sulfide, propylene sulfide, etc.

The reaction appears to involve equimolar proportions of the ammonium orsubstituted ammonium salt of the phosphorodithioic acid and the epoxide.This reaction appears to be unique in that ammonia or an amine isliberated upon addition of an epoxide. Since ammonia and amines arebasic compounds it would not be expected that they would be liberatedfrom their salts by a neutral material such as propylene oxide. Theidentity of the products have not been established other than that theyare known to be hydroxy-substituted triesters and so they are bestdescribed in terms of their method of preparation. The products areneutral, having a phosphorus to sulfur ratio of 1:2, and as indicatedbefore, appear to result from the reaction of one mole each of ammoniumor substituted ammonium phosphorodithioate and epoxide.

It is usually convenient to use an excessive amount of the organicepoxide so as to insure a maximum yield. in most instances the epoxideis sufficiently volatile that its removal from the reaction mixture,after the reaction is finished, is a simple operation. In some cases, itis sufficent merely to allow the excess epoxide to evaporate from theproduct at room temperature, or the product may be flushed with an inertgas such as nitrogen, or subjected to reduced pressure.

The process of the invention is illustrated further in detail by thefollowing specific examples:

Example 1 Dissolved hydrogen sulfide is removed from 660 grams (2 moles)of 0,0'-di(2-methylpentyl-4) phosphorodithioic acid by heating at 30-35C. for 0.5 hour at 30 mm. mercury pressure. An aqueous solution of 170grams (2.2 moles) of ammonium acetate dissolved in 79 grams (4.4 moles)of water is added at 30-48 C. in 0.5 hour. The reaction is mildlyexothermic resulting in a clear yellow-green solution having aneutralization number of 4.5 (basic to bromphenol blue), into which 128grams (2.2 moles) of propylene oxide is introduced at 4048 C. in 0.75hour with external cooling in an exothermic reaction. Stirring iscontinued for 0.5 hour at 48 C. and the reaction mixture is then allowedto separate into layers. The organic phase is stripped at 75 at mm.mercury pressure and is filtered, resulting in 762 grams of product. Theproduct contains 17.14 percent sulfur, 8.21 percent phosphorus, lessthan 0.02 percent nitrogen, 5.3 percent OH and has a neutralizationnumber of 5.80 acid to phenolphthalein.

Example 2 Dry nitrogen gas is passed through a solution of 1980 grams (6moles) of 0,0-di-(2-methylpentyl-4)phosphorodithioic acid for 0.25 hourand then 102 grams (6 .hour. Stirring is continued for 1.5 hours withthe addition of 121 grams (1.9 moles) of sulfur dioxide. The filteredproduct is found to contain 8.39 percent phosphorus, 17.03 percentsulfur, 0.24 percent nitrogen, and to have a neutralization number of 28acid to phenolphthalein.

Example 3 Nitrogen gas is passed through 660 grams (2.0 moles) of0,0'-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25C., followed by the addition of 100 grams of water and 137 grams (2.2moles) of 28% aqueous ammonium hydroxide which is added in 0.5 hour at2150 C. Propylene oxide, 128 grams (2.2 moles) is added below thesurface in 1 hour while 1.6 standard cubic feet (2.2 moles) of carbondioxide is passed into the reaction mixture at 4050 C. with cooling. Themixture is stirred for an additional 0.5 hour at 45 -50 C. and is thenallowed to separate into two layers. The organic layer is heated to 75C. at 100mm. mercury and is then filtered to give 767 grams of productcontaining 8.07 percent phosphorus, 17.47 percent sulfur, 0.021 percentnitrogen, and having a neutralization number of 1 acid tophenolphthalein.

Example 4 Nitrogen gas is passed through 660 grams (2 moles) of0,0"-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25C., and then a solution of 139 grams (2.2 moles) of ammonium formate in150 grams of water is added at 3050 C. in 0.5 hour. The reaction ismildly exothermic resulting in a solution to which is added 128 grams(2.2 moles) of propylene oxide at 4050 C. in 0.75 hour with externalcooling. The reaction mixture is stirred for 0.5 hour to assure completereaction, and is then allowed to stand for 0.5 hour to separate into twolayers. The organic layer is heated to 70-75 C. at 100 mm. mercurypressure and filtered. The filtrate is the product.

Example 5 Nitrogen gas is passed through 660 grams (2 moles) of0,0'-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25C., and then a solution of 231 grams (2.2 moles) of ethylamine acetatein 250 grams of Water is added at 3045 C. in 0.5 hour. The reaction ismildly exothermic resulting in a reaction mixture to which is added 128grams (2.2 moles) of propylene oxide at 40-- 50 C. in 0.75 hour withexternal cooling. The reaction mixture is stirred for 0.5 hour to assurecomplete reaction, and is then allowed to separate into two layers. Theorganic layer is heated to 7075 C. at 100 mm. mercury pressure andfiltered. The filtrate is the product.

Example 6 Nitrogen gas is passed through 660 grams (2 moles) of0,0'-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25C., followed by the addition of a concentrated aqueous solutioncontaining 231 grams (2.2 moles) of dimethylamine acetate in 0.5 hour at21-50 C. Butylene oxide, 159 grams (2.2 moles) is added at 4050 C. in 1hour with cooling. The reaction mixture is stirred for 0.5 hour toassure complete reaction, and is then allowed to separate into twolayers. The organic layer is heated to 75 C. at 100 mm. mercury pressureand filtered. The filtrate is the product.

Example 7 Ammonia gas, 37 grams (2.2 moles) is passed into 708 grams(2.0 moles) of 0,0'-di-iso-octyl phosphorodithioic acid and 20 grams(1.1 moles) of water in 1 hour at 25 60 C. Ethylene oxide, 97 grams (2.2moles) and carbon dioxide, 97 grams (2.2 moles) are introduced beneaththe surface of the resulting salt in 2 hours at 5060 C. with cooling.The reaction mixture is stirred an additional 0.5 hour, and the mixtureis cooled to 25 C. and filtered. The filtrate is the product.

Example 8 To 588 grams (2.0 moles) of 0,0'-di-cyclohexylphosphorodithioic acid, 200 grams (2.2 moles) of ammonium propionate isadded in 0.5 hour at 2150 C. The reaction is mildly exothermic resultingin a solution to which is added 159 grams (2.2 equivalents) of butyleneoxide at 40-50 C. in 1 hour with external cooling. The reaction mixtureis stirred for 0.5 hour to assure complete reaction and is then allowedto separate into two layers. The organic layer is heated to C. at 100mm. mercury pressure and filtered. The filtrate is the product.

Example 9 Dry nitrogen gas is passed for 0.5 hour through aphosphorodithioic acid prepared by reacting 4 moles of a mixture of 65%isobutanol and 35% primary amyl alcohol with 1 mole of phosphoruspentasulfide. An aqueous solution of 340 grams of ammonium acetate (4.4moles) dissolved in 158 grams (8.8 moles) of water is added to 1108grams (4.0 moles) of this phosphorodithioic acid at 30-50 C. for 0.5hour. Propylene oxide, 255 grams (4.4 moles) is added below the surfacein 1 hour at 50 55 C. with cooling. The mixture is stirred for anadditional 0.5 hour at 50 C. and is then allowed to separate into twolayers. The organic layer is heated to 75 C. at 100 mm. mercury pressureand is then filtered. The filtrate is the product.

A useful derivative of the hydroxy-substituted triesters ofphosphorodithioic acids is prepared by the reaction with an inorganicphosphorus reagent selected from the class consisting of phosphorusacids, phosphorus oxides, and phophorus halides. The preferred inorganicphosphorus reagent in the reaction with the hydroxy-substitutedtriesters of phosphorodithioic acids is phosphorus pentoxide. Theproducts of this reaction are acidic materials which in themselves areuseful.

These acidic materials may be further reacted with basic reacting metaloxides or with amines to make other useful products. These are describedmore fully in copencling application No. 130,270, filed Aug. 9, 1961,now US. 3,197,496.

What is claimed is:

1. In the process of preparing a hydroxy-substituted phosphorodithioicacid triester by reacting at a temperature below the decompositiontemperature the ammonium salt of a phosphorodithioic acid having thestructural formula (RO) PSSH-NR wherein R is a hydrocarbon radical and Rhydrogen or hydrocarbon, with at least about an equivalent amount of anepoxide, whereby NR' is formed as a by-product; the improvementcomprising conducting the reaction in the presence of an acidic compoundof lesser acidity than the phosphorodithioic acid of the said salt, saidacidic compound being present in the reaction mixture in an amountsufiicient to remove the NR remaining in the reaction mixture.

2. The improvement of claim 1 wherein the acidic compound has a pKgreater than about 1.

3. The improvement of claim 1 wherein the acidic compound is analiphatic carboxylic acid.

4. The improvement of claim 1 wherein the acidic compound is an aromaticcarboxylic acid.

5. The improvement of claim 1 wherein the acidic compound is aceticacid.

6. In the process of preparing a hydroxy-substituted phosphorodithioicacid triester by reacting at a temperature below the decompositiontemperature the ammonium salt of a phosphorodithioic acid having thestructural formula (RO) PSSH-NH wherein R is alkyl, with an aliphaticepoxide whereby NH is formed as a by-product, the improvement comprisingconducting the reaction in the presence of an acidic compound selectedfrom the group consisting of carbon dioxide, sulfur dioxide and reactionmixture in an amount sufficient to remove the NH remaining in thereaction mixture.

References Cited UNlTED STATES PATENTS 3,284,548 11/1966 Wierber 260953CHARLES B. PARKER, Primary Examiner.

boric acid, said acidic compound being present in the 10 A- H- SUITO,Assistant Examiner.

1. IN THE PROCESS OF PREPARING A HYDROXY-SUBSTITUTED PHOSPHORODITHIOICACID TRIESTER BY REACTING AT A TEMPERATURE BELOW THE DECOMPOSITIONTEMPERATURE THE AMMONIUM SALT OF A PHOSPHORODITHIOIC ACID HAVING THESTRUCTURAL FORMULA (RO)2PSSH$NR''3 WHEREIN R IS A HYDROCARBON RADICALAND R'' HYDROGEN OR HYDROCARBON, WITH AT LEAST ABOUT AN EQUIVALENTAMOUNT OF AN EPOXIDE, WHEREBY NR''3 IS FORMED AS A BY-PRODUCT; THEIMPROVEMENT COMPRISING CONDUCTING THE REACTION IN THE PRESENCE OF ANACIDIC COMPOUND OF LESSER ACIDITY THAN THE PHOSPHORODITHIOIC ACID OF THESAID SALT, SAID ACIDIC COMPOUND BEING PRESENT IN THE REACTION MIXTURE INAN AMOUNT SUFFICIENT TO REMOVE THE NR3 REMAINING IN THE REACTIONMIXTURE.